Skeletal Muscle Contraction Flashcards
Epimysium
Connective tissue surrounding the entire muscle
What is the hierarchical organization of skeletal muscle
Epimysium->Muscle->Perimysium->Fascicle->Endomysium->Sarcolemma->Myofiber->Myofibril->Myofilament (sarcomere)
Muscle components
Made of multiple fascicles
Perimysium
Connective tissue covering individual fascicles
Fascicle
A bundle of myofibers
Endomysium
Connective tissue lining each myofiber
Sarcolemma
Cell membrane of muscle fiber (aka, plasmalemma)
Myofiber
Individual, multinucleated muscle cell (aka, muscle cell)
Myofibril
A chain of sarcomeres within a muscle fiber/muscle cell
Myofilament
Actin and myosin filaments that make up a sarcomere
What do T-tubules do and where are they found?
Found in the sarcolemma, close to the cisternae of the SR… They transport the action potential through the muscle cell
What are the bands of a sarcomere and what do they contain
Z-disc: at ends of sarcomere, anchors actin filaments I-band: composed of only actin, width changes H-band: composed of only myosin, width changes A-band: composed of entire myosin filament and a portion of actin filament, width does not change M-line: formed when H-band brings together actin filaments forming the M-line
Explain the process of muscle contraction
1)Action potential reaches end of axon opening voltage-gated channels releasing ach into synaptic cleft, which open ligand-gated Na+ channels sarcolemma, generating action potential in sarcolemma 2)Action potential in sarcolemma travels down T-tubules to the DHP which interacts with ryanodine-receptors to release Ca++ from SR into cytosol 3)Ca++ binds to troponin which moves tropomyosin off of myosin binding sites on actin and myosin filaments walk down actin filaments 4)Ca++ is pumped back into SR by active transport and also sequestered by calsequestrin
What are DHP receptors
Voltage-gated channels on T-tubules of sarcolemma that cause a change in ryanodine receptors allowing Ca++ to leave SR and enter cytoplasm
What are Ryanodine receptors and SERCA
Ryanodine receptors (RyRs) are on the cisternae of the SR and respond to a conformational change in the DHP receptors allowing Ca++ to flow into the cytoplasm… SERCA= ATPase pump that pumps Ca++ back into the SR
Calsequestrin
Helps maintain the proper Ca++ concentration in the SR and cytoplasm by binding to Ca++ and bringing it back in the SR after contraction
When is there no tension on the muscle
When the sarcomere is fully relaxed and there is no interaction b/w myosin and actin
When does tension on the muscle begin and reach its max
When the actin and myosin begin interacting, tension begins…tension reaches its max when the actin filaments come together and the M-line is formed…after that, tension begins to decrease again
Where is ATP used during muscle contraction
Mainly during sliding filament mechanism…pumping Ca++ back into the SR and Na+ and K+ ions out and into the cell to repolarize the cell
How much ATP is available for contraction…
1-2 seconds worth
How does the phosphocreatine energy system work
It reconstitutes the ATP and provides enough energy for 5-8 seconds of contraction
How does glycolysis contribute to muscle contraction
Allows for ~1 minute of contraction, but causes build up of lactic acid
What is the main energy source for longterm muscle contraction
Oxidative Phosphorylation…accounts for ~95%
Isometric Contraction
Causes increase in tension, but not muscle length
